1. Field of the Invention
The invention relates in general to imaging, gated-video tracker systems and in particular to tracking-gate sizing techniques for such systems. The invention has special relevance in those situations where it is desired to optimize tracker performance against diagonally-disposed high-aspect-ratio targets.
2. Description of the Prior Art
The conventional tracking gates of prior-art imaging, gated-video trackers have been generally rectangular in nature. When attempting to adjust the size of such a rectangular gate so as to more closely conform to the contours of a given tracked target, it has been the usual practice to adjust only the overall length and width of the gate. In other words, the conventional tracking gates have typically been limited to only two degrees of sizing freedom.
This sizing limitation has created difficulties with respect to particular kinds of targets in particular kinds of situations. The targets of concern are those whose length is significantly different from their width. The ratio of a target's length to its width, denominated its aspect ratio, provides a measure of the degree of such length-width discrepancy.
The particular processing situation of concern is that in which a high-aspect-ratio target is presented with its principal geometrical axes diagonally disposed with respect to the principal axes of the tracking gate.
Consider, for example, the situations presented in FIGS. 1 and 2. These figures show a high-aspect-ratio target in various orientations. The figures illustrate the degree to which gate-to-target conformity can be achieved using a merely rectangular gate. As can be seen from FIGS. 1a and 1b, the degree of conformity is quite good in those orientations where the principal axis 120 of the target 110 coincides with a principal axis of the gate 100, this being in the vertical orientation of FIG. 1a and the horizontal orientation of FIG. 1b. However, when the target's axis 120 is diagonally disposed as in FIG. 2, it is apparent that the degree of conformity is rather poor.
FIGS. 2a and 2b illustrate two alternative prior-art approaches to gate sizing in such a diagonality situation. The general attempt to enclose the target 110 in its entirety leads in FIG. 2a to a condition in which significant areas of the gate 200a are open to non-target-related imagery such as the indicated clutter 240. The converse attempt to eliminate the clutter 240 by restraining gate size according to considerations not directly related to actual target extent leads in FIG. 2b to a condition in which significant portions of the target image 100 are excluded from tracker processing. In many situations this can lead in turn to a tracker instability condition in which the track gate 200b tends to first oscillate along the length of the target and then eventually move off the target altogether.
It is an aim of this invention, therefore, to enhance the performance of an imaging, gated-video tracker by improving the degree of gate-to-target conformity between the tracking gate and diagonally-disposed, high-aspect-ratio targets.
An important operational context for such high-aspect-ratio diagonal dispositions in that in which the target is rotating in the field of view while being tracked. With respect to such a context, FIGS. 1a, 2a and 1b could thus be taken as a sequence of target orientations through which track is to be maintained.
It is a further general aim of this invention, therefore, to enhance the performance of an imaging, gated-video tracker with respect to a high-aspect-ratio target which rotates in the field of view while being tracked.